Arc torch

ABSTRACT

A method of establishing an electric arc in an electric arc torch having a cathode unit and a plurality of substantially coaxial bushings. The method comprises flowing an enveloper gas between the cathode unit and the adjacent bushing, establishing an arc between the tip of the cathode and the adjacent bushing, flowing an enveloper gas between the adjacent bushing and the next surrounding bushing, and subsequently shifting the end of the arc from the adjacent bushing to the workpiece and stopping the enveloper gas originally presented between the cathode unit and the adjacent bushing.

United States Patent Inventor Haruo Tateno Tokyo, Japan Appl. No. 733,649 Filed May 31, 1968 Patented Apr. 20, 1971 Assignee Rikagaku Kenkyusho Kitaadachi-gun, Japan Priority June 8, 1967 Japan 42/36720 ARC TORCH 7 Claims, 13 Drawing Figs.

US. Cl 219/75, 219/ 101 Int. Cl 823a 9/16, 823a 9/00 Field of Search 219/75, 121, 121 (P) [56] References Cited UNITED STATES PATENTS 2,799,769 7/1957 Vogel.... 219/75 2,806,124 9/1957 Gage 219/121 3,076,085 l/l963 Sundstrom 219/75 3,250,893 5/1966 Nestor 219/121 Primary Examiner-J. V. Truhe Assistant Examiner'L. H. Bender Att0rneysRalph E. Bucknam, Jesse D. Reingold, Robert R.

Strack and Henry A. Marzullo, Jr. I

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ARC TORCH This invention relates to an electric arc torch.

Electric arc torches are widely used in the fields of welding, cutting, coating and other operations. In these applications it is most important to stabilize the arc flame from the blowpipe. Hitherto, various improvements have been made in the material and structure of the torch as well as the method of generating the electric arc.

A lot of proposals have been made in the hope of making full use of the concentration of heat generated the high temperature of heat and other useful features of the electric arc. These proposals, however, have not been reduced to practice, partly because of difficulty in stabilizing the operation of the torch, and partly because of lack of repeatability of the arc characteristics.

As a consequence of the study of the electric arc, the inventor has discovered that the unstability of the arc flame is mainly attributable to the occasional shift of the cathode spot on the tip surface of the cathode unit of the torch. This invention is based upon this discovery. That is, the stability of the arc torch improves by eliminating the unstable tendency of the cathode spot. The improvement attained permits the arc to be applied to fields wherein hitherto the use of the electric arcing art has been impossible.

Accordingly, the object of this invention is to improve the stability of the electric are from the torch.

This invention will be better understood from the following description which is made with reference to accompanying drawings:

FIG. 1 is a longitudinal section of a conventional inert gastype arc torch;

FIG. 2 is a longitudinal section of an arc torch according to this invention;

FIG. 3a is a longitudinal section of an embodiment of this invention. using an active or molecular gas stream as an enveloper;

FIG. 3b is a longitudinal section of another embodiment using an active plasma stream as an enveloper;

FIG. 4a shows the torch according to this invention and an external electric circuit which is used to facilitate the operation of the torch operation;

FIGS. 4b and 40 show modifications of the external electric circuit as shown in FIG. 4a;

FIG. 5 is a longitudinal section of an embodiment of the torch using a jet stream of plasma;

FIG. 6 is a longitudinal section of a modification of the torch as shown in FIG. 5, the modification being capable of controlling the arc voltage;

FIG. 7 shows a modification of the torch as shown in FIG. 6, the modification permitting the increase of the ratio of molecular gas to protecting gas;

FIG. 8 is a longitudinal section of an embodiment which is suited for generating a curved arc;

FIG. 9 shows a modification of the torch as shown in FIG. 8, the modification being capable of varying the direction of the arc;

FIG. 10 shows a modification suitable for use on an object consisting of portions of different heat capacities.

Firstly, explanation is made on the cause for the unstable operation of the conventional torch.

Referring to FIG. I which shows the conventional inert gastype are torch, the electric are I is established between a cathode unit 2 and an article or object 3 to be worked. An enveloper stream 4 is supplied from an inlet 5, and flows along the inner surface of a bushing 6 for the purpose of preventing the cathode unit and the workpiece from being oxidized. Usually, argon or helium is used as an enveloper gas. The reference numeral 7 indicates a cathode holder.

The shape of the cathode unit 2 is an essential factor for stabilizing the electric arc. Usually, the cathode unit is polished to a point at its exact top center. Argon gas used as an enveloper should be very pure, and consist of 99.8 percent or more argon, 0.05 percent or less oxygen, ml./m. or less water. Even if such pure argon is used as an enveloper gas, since the cathode unit is locally heated in the vicinity of the cathode spot, the localized heating advances the chemical reaction between the cathode metal and the small impurity content of the argon, and as a result the cathode is gradually consumed. In the region wherein the cathode unit is locally heated at 600l,000 C., an oxide having a high vapor pressure, is produced. The production of such an oxide causes the cathode to be badly consumed and deformed. The deformation thus made in the vicinity of the cathode spot causes disturbance in the gas stream. The unstability of the arc is found to originate from the disturbance in the gas stream along with the deformation in the cathode member. As is apparent from the foregoing, the unstability of the arc flame is caused by:

l. The local deformation of the cathode in the vicinity of the cathode spot, and

2. the disturbance in the gas stream due to the deformation of the cathode above.

The first embodiment of this invention as shown in FIG. 2 has a cathode bushing 9 electrically insulated from the cathode 2 by means of an insulator 8. The cathode 2 is positioned within the bushing 9. The tip of the cathode reaches short of the end of the bushing. The bushing 9 made from copper or an arc-resistant metal such as silver-tungsten alloy, is water-cooled. (For the simplicity of illustration the water cooling device is not shown.) An outer cathode bushing 6 encircles the cathode bushing 9. An enveloper gas stream II is supplied from an inlet 10 and flows between the cathode 2 and the cathode bushing 9. Another enveloper gas is supplied from an inlet 4 and flows between the inner bushing 9 and the outer bushing 6. DC voltage is applied to the cathode 2 and the work member 3 by an electric source S, and a highfrequency voltage is generated and superimposed on the DC voltage via an air-core inductor T from a highfrequency generator H.F. Then, an are 1 is established between the cathode tip and the work member. Immediately after the arc has been established, the supply of one of the enveloper gas streams, that is, the supply of the gas stream 11 is ceased, and consequently, only the other enveloper gas stream 4 continues to flow. There is no gas stream flowing around the cathode unit during operation. As is apparent from the explanation so far, the essential feature of this invention resides in that:

No gas stream is provided around the cathode during operation.

During operation, the supply of the enveloper gas 11 is ceased, as mentioned above. The tip of the cathode 2 is positioned within the cathode bushing 9. Thus, the gas left around the cathode within the bushing is separated from the outer enveloper gas stream. The small amount of impurities present in the remaining gas within the bushing, will chemically act on the material of the cathode unit. As a consequence of the chemical reaction the remaining gas will be made inactive to the metal of the cathode. Thus the ceaseless consumption of the cathode which would be found in case of the sensual of impurities by the continuous supply of the gas stream, will be fully avoided. If the cathode unit is partly consumed and deformed in the vicinity of the cathode .spot because of the localized overheating and/or a lot of residual impurities, the deformation of the cathode unit will not adversely affect the stability of the cathode spot, because there is not any gas stream which would be disturbed due to the deformed part of the cathode.

The are torch according to this invention has a remarkable advantage in industrial application, as will be apparent from the following.

With a view to protecting the cathode from the active gas or to lowering the arc voltage, it is a common practice in the art to flow over the surface of the cathode an inert gas such as argon, which is chemically inactive to the cathode material and has a low cathode drop.

In the conventional plasma jet torch using an active gas (such as air) or a molecular gas (nitrogen, hydrogen) for the main gas stream, the cathode cannot be fully protected without using a relatively large amount of protecting gas (15- 20 percent of the amount of the main gas), because of the rapid and intense mixing of the main and protecting gases.

in this invention, as seen from FIGS. 3 and 7, the protecting gas stream 11 and the main gas stream 14 are separated and flow in the laminar form, so that the arc is stabilized. The amount of the protecting gas sufficient to protect the cathode is reduced to approximately 5 percent of the main gas.

The reduction in the amount of the protecting gas, such as argon permits the reduction of the unit cost of operation because the price of the protecting gas is three times higher than the molecular gas (hydrogen, oxygen, nitrogen and the like).

According to this invention the arc can be curved and used in a stable state. it is commonly known in the production of the plasma jet torch that the accurate machining of the gap between the cathode surface and the anode wall is an essential factor for the stability of the arc. in this invention, however, the arc path is determinated only by a reduced port 12. In other words, the stability of the arc does not depend upon the accuracy with which the gap between the cathode 2 and the cathode bushing 9 and the gap between the cathode bushing 9 and the gas stream bushing 12 are made. This permits the easy production of the torch and the manufacture of the modifications as shown in FIGS. 8 and 9.

The essential factors to make the torch according to this invention are the cooling of the cathode bushing and properly setting the distance from the tip of the cathode to the end of the cathode bushing (hereinafter referred to as the "distance to the cathode tip").

in the embodiment as shown in FIG. 2, argon is used as an enveloper gas, and the arc is established with the electric current of 200-08 a. When the "distance to the cathode tip" varies within the range from 0.5 to 4.0 mm., the arc voltage varies from 15 to 25 v./cm. The electric power due to the potential drop in the arc is consumed to heat the cathode bushing. Therefore, the cooling of the bushing must be intensified with the increase of the electric current. if the cooling is insufficient, the end of the bushing will be heated until another are will be established between the end of the bushing and the work member.

The determination of the distance to the cathode tip depends upon the disturbance in the outer gas stream 14, the pressure of the gas and other factors. The stability of the arc improves with the increase of the distance to the cathode tip. in this connection it is preferable to set the distance at the minimum value necessary in stabilizing the are (approximately l2 mm.

Various examples given below are directed to the torch using a cathode rod of a small diameter. Such a torch is liable to be badly damaged and deformed, and therefore, the improvement attained by this invention would be better understood from such examples. However, it should be noted that this invention can be applied to the torch having a cathode rod of a large diameter.

Embodiment 1 This example relates to the arc torch which is suitable for use in arc welding. A small electric current torch is suitable for welding copper or stainless steel thin plates or tubes as thick as 0.1 mm. or less, connecting aluminum or copper fine wires and soldering workpieces of large heat capacity. The unstability of the torch has hitherto prevented its use in the operation as mentioned above. In the torch of this invention as shown in FIG. 2, a tube of copper or silver-tungsten alloy having an inner diameter of 1.7 mm. and an outer diameter of 3.0 mm. was used as the cathode bushing 9, whose bottom was cooled by the circulation of water. A copper tube having an inner diameter of 4.0 mm. was used as the outer bushing 6, to which is applied the same potential as the cathode bushing 9 (of course, the use of the heat resistant ceramic bushing as is the case with the conventional torch, does not adversely affect the performance of the torch). The diameter of the cathode was determined at 1.0 mm. for the electric current from 5 to 10 a., 0.5 mm. for the current from l to 5 a. and 0.3 mm. for the current form 0.8 to l a. The top of the cathode was shaped into a cone whose vertical angle is equal to 30. The distance to the cathode tip" was set at 2.5 mm. in each of the torches. Argon was used as an enveloper gas, and the flow rate of the enveloper gas was set at 0.5 l/min. In the range of the electric current above mentioned, the test operation was continued for the period of 8 hours. The operation was quite stable except for an appreciable variation caused by the unstability of the electric source.

Thin steel plates 0.1 mm. thick were welded with 2 a. are current and 0.5 l/min. argon. Copper pipes having a diameter of 1.0 mm. and thickness of 0.05 mm. were welded in abutment with 0.6 a. are current and 0.5 l/min. argon. Thin stainless steel plates 0.1 mm. thick were welded with 4 a. are current and 0.5 l/min. argon. An excellent result was obtained with every test.

An airtight connection was obtained by soldering with the arc torch. The are flame was positioned 0.5l.0 mm. apart from the surface of the workpiece, and solder was supplied at a high rate. The are current was 2--4a. Argon was supplied at a rate of 0.5 l/min.

Embodiment 2 This example relates to the torch using as an enveloper, a gas active to the cathode material or a molecular gas. it is well known that the use of a molecular gas (such as nitrogen, hydrogen or carbonic acid gas) as an enveloper causes the extreme concentration of the heat generated to the anode spot on the workpiece and simultaneously to the cathode spot on the cathode tip. The localized overheat originating from the heat concentration to the cathode spot has been completely overcome by the torch as shown in FIG. 3a. Like parts of this embodiment are indicated by like reference numerals in FIG. 2; This embodiment is so constructed that a gas stream bushing 12 is provided around the cathode bushing 9 (outer diameter 2.5 mm.; inner diameter 1.7 mm.). A protecting gas 4 flows from an inlet 5 to the surface of the workpiece via the annular space between the cathode bushing 9 and the gas stream bushing 12.

Similarly, there is provided an outermost bushing 6 (inner diameter 5.0 mm.) around the bushing 12. A main gas 14 (molecular gas) flows from an inlet 13 to the surface of the workpiece via an annular space between the bushings 12 and 6. The position and shape of the cathode unit is the same in FIG. 2.

Argon gas (200 c.c./min.) was used as the protecting gas 4, and hydrogen gas (2 l/min.) was used as the main gas 14. A workpiece 3 was cooled by circulation of water. The distance between the end of the gas stream bushing '12 and the workpiece 3 was approximately 1 mm. The arc current was within 2 l0a., and the arc voltage was within 60-45v. When nitrogen or carbonic acid gas was used, the arc voltage was within 50-40v.

The above torch using hydrogen gas was used to weld an aluminum plate 0.5 mm. thick. The welding rate was approximately l5 m/hr.

Embodiment 3 This embodiment relates to an arc torch using an active plasma stream.

The operation using a chemically active gas and an electric arc flame in combination, such as oxygen arc cutting or oxygen-argon are cutting (l520 percent oxygen gas content) is noted for its high efficiency and wide applicability. Such operation can be used in cutting any kind of metal, and under water. The defect of this operation, however, is the consuming of the cathode unit.

The embodiment of FIG. 3b overcomes this problem. The torch of FIG. 3b is the same as the torch of FIG. 3a except for the converging end of the outermost bushing 6. The restricted aperture 6' thus made functions to produce a plasma stream.

Oxygen gas or air was supplied at the rate of 3 l/min., and used as the main gas stream 14. Argon gas was supplied at the rate of 0.4 l/min., and was used as the protecting gas. The workpiece 3 was a copper tube, which was slowly rotated during operation. The are current was selected within 5--- lOa. The are flame was stable for the operation period of 8 hours.

The provision of the gas stream bushing having a converging end permits stable operation even in the plasma stream which, otherwise, is liable to bring about an extreme intensified chemical reaction at the cathode. The cathode unit of the torch was then found to be unconsumed in either method of operation stated above.

The convergent end of the outer bushing (I2 in FIG. 3a, or 6 in FIG. 3b) functions to reduce the cross section of the arc flame I, as is the case with the conventional plasma jet torch. If the end of the innermost bushing 9 is made convergent, the cathode bushing 9 will function to reduce the cross section of the arc flame, and, then, the convergent end of the outer bushing will function to direct the flame.

Embodiment 4 This embodiment relates to an arc torch which facilitates operation. In using the arc torch as shown in FIG. 2 or FIGS. 30 and 3b, the operation cannot be interrupted without extinguishing the arc flame; It is inconvenient to start and stop the are at the beginning and end of each successive operation, and especially inconvenient to start and stop the gas stream.

This problem has been completely overcome by the torch as shown in FIG. 4a. The torch of FIG. 4a is the same as the torch of FIG. 3 except for the provision of an insulator I5 electrically insulating both of the gas stream bushing 12 and the outer bushing 6 from the cathode bushing 9, and the provision of an electric circuit having contacts a, b and c.

The operation of the torch of FIG. 4a is as follows:

Firstly, gases are supplied from the inlets l0 and 5. Then the supply of the gas from the inlet I0 is ceased, while the gas stream 4 continues to flow. The electric source S is connected through the contact a to the torch. Then, an electric potential is applied between the cathode unit 2 and the cathode bushing 9. As a result, an electric arc is established between the top of the cathode unit 2 and the inner surface of the cathode bushing 9. The are thus produced is within the cathode bushing wherein there flows no gas stream. The gas stream 4 flowing in the annular space between the cathode bushing 9 and the gas stream bushing 12, is heated by a part of the arc leaking from the cathode bushing and as a consequence, there appears the heated and ionized gas around the end of the cathode bushing. The contacts a and b are both connected to the electric source S, and then the contact a is disconnected from the electric source S. As a result, the anode spot of the arc is shifted from the end of the cathode bushing 9 to the end of the gas stream bushing I2. The are thus shifted is within the flowing gas stream, and therefore the plasma jet flame is produced. The space between the top of the cathode unit 2 and the surface of the work piece 3 is conducting because of the presence of the plasma jet flame. The contacts b and c are both connected to the electric source S, and then the contact b is disconnected from the source S. As a result, the are is shifted and established between the cathode unit 2 and the work piece 3.

The reverse operation on the contacts will cause the shift of the arcin reverse.

The following two advantages can be obtained from the modification of FIG. 4a and the accompanying electric circuit.

Firstly, the intermission of the are extending to the workpiece can be effected without extinguishing the are extending from the cathode unit.

Secondly, the plasma flame is completely confirmed within the cathode bushing containing no flowing gas stream. In other words, no plasma flame leaks from the cathode bushing, and therefore useless heating of the workpiece can be fully avoided.

Also, the light from the cathode spot can be used to illuminate the surface of the workpiece. The illumination by means of the cathode spot is useful particularly in welding, for instance, fine wire.

In the operation as mentioned above it should be noted that the transition of the anode spot of the arc to the next outer bushing will fail unless the path from the cathode tip to the edge of the next outer bushing is made conductive under the influence of the gas heated and ionized by the arc.

In this connection it is necessary to flow the gas between the inner bushing and the next outer bushing to which the anode spot is to be shifted, before applying an electric potential to the next outer bushing.

The increase of the distance to the cathode tip is effective in stabilizing the arc. But, if the distance is increased, the transition of the anode spot fails, because the outer gas stream in the vicinity of the edge of the next outer bushing is not fully heated and ionized, and therefore, the path to the edge of the next outer bushing is made less conductive.

This tendency, however, can be improved by planing off the inside edge of the aperture of the inner bushing so as to allow a small part of the gas flowing along the outer surface of the inner bushing to enter the inner bushing, thereby assuring the contact between the arc and the gas.

As for the actual device which is later referred to, the possible maximum distance to the cathode tip" was approximately 0.8 mm., but this FIG. could be improved to be 1.5 mm. with the cathode aperture (3 mm. 1 having the inside annular'edge planed off at 15.

With a view to stabilizing the cathode spot and assuring the transposition of the anode spot, the distance to the cathode tip is usually determined to be shorter by approximately 0.1- 0.2 mm. than the critical distance.

With the torch as shown in FIG. 4a the operation can be interrupted without extinguishing the arc flame. Thus, the operation is made easy and efficient.

Referring to FIGS. 4b there is shown a modification of the electric circuit of FIG. 4a. The modification is suitable for use in the operation on a relatively small work piece wherein the working electric current must be smaller than the arc sustaining electric current. The working electric current is supplied from a reactor type electric source of relatively small capacity, while the arc sustaining electric current is supplied from another reactor type electric source of relatively large capacity. The electric sources have a drooping characteristic. The advantages of the modification over the electric circuit using a single source capable of supplying both of currents are the high efficient use of the electric source, and the capability of transporting the operation to a different workpiece while maintaining the arc in the torch.

Referring to FIG. 40 there is shown another modification, which is suitable for use in the operation on a relatively large workpiece wherein the working electric current must be larger than the arc sustaining electric current.

Contrary to the precedent modification, the electric source S is of a small'capacity and the electric source S is of a large capacity. A constant current type power supply is used as the electric source 8,, and a constant current or voltage type power supply is used as the electric source S In this modification the arc sustaining current through contact b is decreased by the amount corresponding to the working current. If the working current is equal to the arc sustaining current, there is no current flowing through the contact b, as is the case with the embodiment of FIG. 4a.

In either of the modifications above, the working current is made variable from zero. With the torch using the electric circuit of FIG. 40 reverse polarity operation is possible.

In the actual device of FIG. 4c, the caliber of the arc path aperture of the bushings 9 and 12 was set at 1.7 mm. Argon gas was supplied from the inlet 5 at the rate of 0.5 l/min. The end of the torch was positioned apart from the surface of the workpiece by 1.0 mm. When the arc current was 5a., the arc voltage of the arc established between the cathode tip and the cathode bushing 9 was v., and there was no plasma flame leaking out of the cathode bushing. Then, the arc was shifted to the end of the bushing 12. The are voltage was 22v. The plasma flame ejected. When the positive potential was applied via the contact C to the workpiece 3, the arc extended and reached the surface of the workpiece. If the distance between the end of the torch and the surface of the workpiece was below 5 mm., the arc could be shifted to the surface of the workpiece without fail simply by the operation on the contacts a, b and c.

Embodiment 5 This embodiment relates to the arc torch generating a plasma jet. The accurate centering of the cathode unit and the gas passage around the cathode unit has been hitherto regarded as being indispensable in stabilizing the operation of the torch. In this connection the tolerance in manufacturing the torch becomes close with the decrease of the size of the torch. Also, it is difiicult to reproduce the stable torch having a common performance.

This problem has been overcome by the embodiment of FIG. 5. It has an anode bushing 6 in place of the outer bushing 6 in the embodiment of FIG. 2. The anode bushing has a narrow end aperture or an anode aperture 6. The anode bushing is insulated from the cathode bushing 9 by an insulator 15.

In the structure as mentioned above, the outer diameter of the cathode bushing was set at 4.0 mm., the inner diameter of the anode bushing 6 was set at 5.0 mm., the diameter of the anode aperture 6' was set at I mm. The axis of the anode bushing 6 was displaced with respect to the axis of the cathode unit so that the annular gap through which the gas stream 14 flows has the right cross width of 0.8 mm. and the left cross width of 0.2 mm. Argon gas as the gas stream 14 was supplied at the rate of 0.5 l/min. The other factors were the same as in Embodiment 2. The arc voltage was 21v. for the arc current of 5a. The arc remained quite stable for the period of over 4 hours. The are voltage was lower by approximately 2v. than the arc voltage of the arc in the torch whose anode bushing was centered at the axis of the cathode unit, and there was found an appreciable decrease in the jet of the plasma flame. The displacement above is impossible or much greater than the probable displacement which would cause in manufacturing the torch. Although the provision of an insulator between the cathode unit and the anode bushing deteriorate the accuracy in manufacturing the torch, most probable displacement is within the range from 0.1 to 0.2 mm. This most probable displacement which was expected in the torch of FIG. 5 causes no adverse effect on the arc voltage and the plasma flame. A torch having an anode bushing of inner diameter of 5 mm. I and another torch having an guide bushing of inner diameter of 6 mm. CD were tested with respect to their performance or characteristics. The test revealed the fact that both of the torches have a common performance or characteristics.

As seen from the foregoing, the misalignment between the cathode unit 2 and the cathode and anode bushings in the torch of FIG. 5 causes no adverse effect on the stability of the plasma flame.

Embodiment 6 This embodiment is a modification of the torch of FIG. 5, and is capable of controlling the arc voltage. In the torch of FIG. 5, the arc voltage depends on the distance between the cathode tip 9 and the inner side of the anode aperture 6. If the distance is increased in the hope of increasing the arc voltage, the arc voltage will not increase proportional to the distance beyond a certain value, and the jet of the plasma flame will be deteriorated. This implies the curving of the arc in the anode aperture. Also, in the conventional plasma torch the structure of the torch can be partly modified with a view to improving the arc voltage. But, such modification cannot be made without accompanying unstability of the are.

This problem has been overcome by the torch of FIG. 6. This embodiment is the same as the embodiment of FIG. 5 except for the provision of a gas stream bushing 12 having a reduced aperture 12'. A common potential is applied to the cathode bushing 9 and the gas stream bushing 12. The are voltage can be increased by increasing the distance between the outer surface of the top end of the gas stream bushing 12 and the inner surface of the top end of the bushing 6. Several torches having different distances between the end of the bushing 12 and the end of the bushing 6 (0.5 mm. to 4.5 mm.) were tested.

The following factors were common to all of the torches tested.

The are voltages of the torches thus tested for the 5 a. current were within the range from 22 v. to 40 v. The test revealed the fact that the arc voltage could be improved at the rate of approximately 4 v./mm. by varying the distance between the ends of the two outer bushings. The jet of the plasma stream 1 was extended with the increase of the arc voltage.

As seen from the above, the reduced aperture 12' of the gas stream bushing 12 functions to stabilize the arc, and any are voltage can be obtained by properly selecting the distance between the top ends of the two outer bushings.

Embodiment 7 This embodiment is a modification of Embodiment 6, and relates to a torch capable of operating at a relatively large ratio of the molecular gas to the protecting gas. The structure of this modification is the same as the torch of FIG. 6, but the diameter of the aperture 12 of the gas stream bushing 12 is selected to be .equal to that of the aperture of the cathode bushing 9.

If the diameter of the aperture 12 is reduced in the torch of FIG. 6 with a view to improving the stability of the are then there is the fear of appearance of a double arc, which bridges the gap between the cathode tip and the inside of the convergent end of the bushing 12, and the gap between the outside of the convergent end of the bushing 12 and the inside of the convergent end of the bushing 6. Then, the convergent ends of the bushings 6 and 12 will be damaged. In order to prevent such double arcing, it is necessary to increase the flow rate of the protecting gas 4 with the decrease of the diameter of the aperture 12'. For example, the diameter of the aperture 12 is approximately 1.0 mm., and if the flow rate of the protecting gas is reduced below 0.4 1/mm., for the 5 a. electrical current, the double arc appears.

The efficiency of the torch, however, will be decreased with the increase of the protecting gas, because the molecular gas rather than the protecting gas must be heated.

Contrary to the foregoing, if the diameter of the aperture 12 is increased with a view to preventing the double arcing, a part of the molecular gas will enter the cathode bushing and chemically react on the cathode unit, resulting in the consuming of the cathode unit.

For the improvement of the efficiency and the full' protection of the cathode the optimum diameter of the aperture 12 has been experimentally determined to be equal to the diameter of the aperture of the cathode bushing.

It should be noted that the thickness of the convergent end of the bushing 6 must be increased to prevent the leaking of the are from the end of the bushing 6.

In the actual example of the torch of FIG. 7, the diameter of the aperture of the gas stream bushing 12 was approximately 1.7 mm., the diameter of the anode aperture 6' was approximately l mm. Argon gas as the protecting gas 4 was supplied at the flow rate of approximately 200 cc./min., and nitrogen gas as the molecular gas was supplied at the flow rate of approximately 2 l/min. The arc current was approximately 4-5a., and the arc voltage was approximately 5045v. The thickness of the convergent end of the bushing 6 must be approximately 3 mm. or more. (The thickness of the corresponding part of the actual torch of FIG. 6 was approximately 0.5-1.0 mm.)

Embodiment 8 This embodiment relates to a torch capable of producing a current are in a stable state. The torch is useful, for instance, in the operation on the inside surface of a tube. Such operation has been hitherto regarded as being impossible.

Referring to FIG. 8, an outlet aperture 12' of the gas stream bushing 12 is angularly positioned with respect to the axis of the cathode unit 2 (for example, at 90 in FIG. 8) so that the are 1 may be bent by the gas stream flowing out from the outlet 12'. The protecting gas stream 14 functions to prevent the working surface of the workpiece from being oxidized.

In an actual torch of FIG. 8, the diameter of the outlet 12 was approximately l.5 mm. Argon gas was supplied from the inlet at the rate of 0.5 l/min. Firstly, the arc was established between the cathode unit 2 and the cathode bushing 9, and then the anode spot of the are thus established was shifted to the workpiece. After the arc was established between the cathode and the workpiece, the supply of the gas stream 11 was ceased.

The curved are thus established was quite stable. For the 5 a. current the arc voltage was higher than the arc voltage would be in the torch having an outlet positioned on the axis of the cathode unit.

FIG. 9 shows a modification of the torch of FIG. 8. The modification is capable of controlling the direction of the curved are by means of a rotatable bushing assembly without moving the whole torch. The rotatable bushing assembly consists of the outer and inner bushings 6 and 12, while are electrically insulated from each other by an insulator 15. The outlets 6' and 12' of these bushings are aligned with each other.

Transposition of the anode spot of the are between the outer bushing and the workpiece can be effected simply by applying an electric potential to either of the'outer bushing and the workpiece. The controlling capability of arc transposition and are direction facilitates the operation.

Embodiment 9 This embodiment relates to an arc torch which is useful in the operation on a workpiece having different heat capacities. The operation of welding such workpiece is extremely difficult.

Assuming that the two conventional torches as shown in FIG. 1 are arranged with their cathode tips directed to two adjacent difierent metal workpieces, and are used to weld and joint these workpieces along their abutment surface, then the two arcs are liable to close to each other, resulting in the formation of a single arc. Therefore, it is extremely difficult to independently heat the two adjacent workpieces by the two different arcs.

The difficulty can be fully avoided by the torch of FIG. 10. As seen from FIG. 10, a shield member intervening between the two cathode units 2 functions to separate and direct the two arcs l to the two adjacent different metal workpieces. The enveloper gas 14 is supplied through the annular space between the cathode bushing 9 and the outer bushing 6. The intensity of the arc depends upon the heat capacity of the workpiece.

In the actual torch of FIG. 10, the two cathode units were positioned with the extensions of their axes meeting at the angle of 25. The distance between the centers of the two cathode apertures 9 at the end of the cathode bushing 9 was approximately 3 mm. Argon gas as the enveloper 14 was supplied at the rate of approximately 1 l/min. A copper sheet approximately 1 mm. thick and another copper sheet approximately 3 mm. thick were silver-welded along their abutment by flowing the arc current of 1.5 a. to the thin sheet and the arc current of 5a. to the thick sheet. The perfect airtight weld was easily attained.

When the access of the torch to a workpiece is difficult, the arcs will extend and the skirts of the arc will expand, resulting in the formation of a combined single are.

Such difficulty is encountered, for example, in welding and fixing a pipe on a thick plate. The extension of the shield end as shown by the broken line in FIG. 1 is effective in preventing the two arcs from being mixed in the operation mentioned above. The size and shape of the extension may be selected so as to fit the working space.

Having thus described my invention, I claim:

I. A method of establishing an electric arc with a torch having a cathode unit and a plurality of substantially coaxial bushing surrounding said unit and spaced from said unit and each other, comprising flowing an enveloper gas between said cathode unit and the adjacent bushing, establishing an are between the tip of said cathode and said adjacent bushing, flowing an enveloper gas between said adjacent bushing and the next surrounding bushing and subsequently shifting the end of said are from said adjacent bushing to a workpiece, wherein the flow of enveloper gas between said cathode unit and said adjacent bushing is terminated after the arc is established with said last-mentioned gas.

2. A method of electric arc welding according to claim ,1, wherein the enveloper gas flowing between said cathode unit and said adjacent bushing is chemically inactive to the cathode material and enveloper gas flowing between said adjacent bushing and the next surrounding bushing is chemically inactive to the cathode material.

3. A method of establishing an electric arc with a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, establishing an arc between the tip of said cathode unit and a workpiece, and stopping the flow of said first enveloper gas, after the arc is established between the tip of the cathode and the workpiece.

4. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, establishing an arc, between the tip of said cathode unit and said adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, shifting the end of said are from said adjacent bushing to said next surrounding bushing, stopping the flow of the first enveloper gas, and shifting the end of said are from said next surrounding bushing to a workpiece.

5. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, establishing an are between the tip of said cathode unit and said adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, shifting the end of said are from said adjacent bushing to a workpiece via said next surrounding bushing, and stopping the flow of the first enveloper gas.

6. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising simultaneously flowing a first enveloper gas between the unit and spaced from said unit and each other, comprising simultaneously flowing a first enveloper gas between said cathode unit and the adjacent bushing and a second enveloper gas between the adjacent bushing and the next surrounding bushing, establishing an are between the tip of said cathode unit and said adjacent bushing, shifting the end of said are from said adjacent bushing to a workpiece via said next surrounding bushing and stopping the first enveloper gas while leaving the second enveloper gas flowing around the arc. 

1. A method of establishing an electric arc with a torch having a cathode unit and a plurality of substantially coaxial bushing surrounding said unit and spaced from said unit and each other, comprising flowing an enveloper gas between said cathode unit and the adjacent bushing, establishing an arc between the tip of said cathode and said adjacent bushing, flowing an enveloper gas between said adjacent bushing and the next surrounding bushing and subsequently shifting the end of said arc from said adjacent bushing to a workpiece, wherein the flow of enveloper gas between said cathode unit and said adjacent bushing is terminated after the arc is established with said last-mentioned gas.
 2. A method of electric arc welding according to claim 1, wherein the enveloper gas flowing between said cathode unit and said adjacent bushing is chemically inactive to the cathode material and enveloper gas flowing between said adjacent bushing and the next surroundinG bushing is chemically inactive to the cathode material.
 3. A method of establishing an electric arc with a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, establishing an arc between the tip of said cathode unit and a workpiece, and stopping the flow of said first enveloper gas, after the arc is established between the tip of the cathode and the workpiece.
 4. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, establishing an arc, between the tip of said cathode unit and said adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, shifting the end of said arc from said adjacent bushing to said next surrounding bushing, stopping the flow of the first enveloper gas, and shifting the end of said arc from said next surrounding bushing to a workpiece.
 5. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising flowing a first enveloper gas between said cathode unit and the adjacent bushing, establishing an arc between the tip of said cathode unit and said adjacent bushing, flowing a second enveloper gas between said adjacent bushing and the next surrounding bushing, shifting the end of said arc from said adjacent bushing to a workpiece via said next surrounding bushing, and stopping the flow of the first enveloper gas.
 6. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising simultaneously flowing a first enveloper gas between the cathode unit and the adjacent bushing and a second enveloper gas between said adjacent bushing and the next surrounding bushing, establishing an arc between the tip of the cathode unit and said adjacent bushing, shifting the end of said arc from said adjacent bushing to said next surrounding bushing, stopping the flow of the first enveloper gas, and shifting the end of said arc from said next surrounding bushing to a workpiece.
 7. A method of operating a torch having a cathode unit and a plurality of substantially coaxial bushings surrounding said unit and spaced from said unit and each other, comprising simultaneously flowing a first enveloper gas between said cathode unit and the adjacent bushing and a second enveloper gas between the adjacent bushing and the next surrounding bushing, establishing an arc between the tip of said cathode unit and said adjacent bushing, shifting the end of said arc from said adjacent bushing to a workpiece via said next surrounding bushing and stopping the first enveloper gas while leaving the second enveloper gas flowing around the arc. 